The invention relates to a method and an apparatus for determining the duration of injection control pulses used to actuate electromagnetic fuel injection valves in an internal combustion engine. The injection valves are opened at times which are synchronous with crankshaft rotations and the length of the time of injection is derived substantially from the magnitude of the air flow rate and from the engine speed (rpm).
Known in the art are fuel injection systems in which the injection control pulse is formed by a monostable multivibrator including a capacitor in a feedback path. In order to obtain a first approximation to a datum defining the fuel injection period, there is disposed within the induction channel of the engine an air flow rate meter of any suitable construction but so embodied as to produce an electrical signal corresponding to the quantity of air taken in by the engine per unit time. In order to obtain an approximately stoichiometric metering of fuel, the signal which is proportional to the air flow rate must be divided by the number of suction strokes per unit time, i.e., by the rpm n of the crankshaft. In the known system, the capacitor in the feedback path of the multivibrator is charged with a constant charging current during a time which is inversely proportional to the crankshaft rpm and, after triggering at a point depending on the rpm, it is discharged with another constant current but one whose magnitude is inversely proportional to the air flow rate. The duration of the discharging process of the capacitor is a measure of the length of the injection pulses.
When fuel injection systems of this type are employed in engines, it is usually necessary to adapt the system to the particular type of engine, and to provide possibilities for adapting the system to the particular number of cylinders in the engine as well as for making other adjustments and connections.